Safety paper and process of preparing the same



Patented Mar. 9, 1943 SAFETY PAPER AND PROCESS OF PREPARING THE SAMEBurgess W. Smith, Rochester, N. 1%, assignor to The Todd Company, Inc.,Rochester, N. Y., a corporation of New Yorlr No Drawing. ApplicationSeptember 26, 1940, Serial No. 358,523

12 Claims.

This invention relates to safety paper, and it comprises a safety paperhaving incorporated therein a 3,3 benzidine derivative reactive withpotassium permanganate solutions to form colored compounds which arestable, especially to heat, and which are resistant to reduction bysodium bisulfite. It further comprises safety paper having distinctivemarking or indicia printed thereon by inks containng such benzidinederivatives, and it further comprises inks suitable for the prmting ofsafety paper, which inks contain benzidine derivatives of the characterdescribed.

Safety paper for makin bank checks, drafts, bonds or other documents arecomposed of a paper base impregnated with chemicals which developdiscoloration upon the application of chemical ink eradicators. Thisimpregnation may be throughout the paper or it "may be the result ofprinting warning indicia, such as the word void," n the paper so thatwhen ink eradicators are applied for the purpose of altering thedocument the chemicals are converted to colored compounds. If, forexample, the word void is printed with a colorless ink, or the printingis camoufiaged when slightly discernible, as shown, for example, in theSmith Patent 1,689,302, then when chemical ink eradicators are appliedthe word void flashes up in color.

Various color-forming compounds have been used in the past forpreparation of safety paper of this type, and the impregnating chemicalshave generally been adequate for the development of a permanent colorwith solutions of hypochlorites preceded or followed by the action of anorganic acid, such as tartaric. Safety papers which contain aromaticamines, such as benzidine, and phenol compounds, such as diphenols,together with manganese sulfate, produce more or less permanent stainswith eradicators of the hypochlorite type. Potassium permanganate willalso form a colored oxidation product with amines and phenols but thiscolored oxidation product can be bleached .with reducing agents, such assodium bisulphite. Moreover, many of the colored oxidation productsobtained by means of potassium permanganate will sublime when heatedmoderately, because of their quinone character, and they can be drivenoff from the paper by warming the paper below the charring temperaturethereof.

Thus the usual aromatic amines and phenolic compounds are satisfactorywhen hypochlorite ink eradicators are used, but are unsatisfactory whenink eradicators of the permanganate type are used. Since potassiumpermanganate is cheap and readily available it is sometimes used for thepurpose of altering documents, and if the safety paper used for thesedocuments is not resistent to the bleaching or volatilization of thecolored permanganate oxidation product then, of course, the paper islimited in its protection.

I have now discovered a class of organic compounds which can beincorporated in safety paper, or in inks for the printing of warningindicia thereon, and which overcome common objections hithertoencountered with respect to eradication by permanganates.

The class of compounds I use can be generically defined as substantiallycolorless 3,3 disubstituted benzidines, or salts thereof, which yield001- ored compounds when treated with potassium permanganate, but whichcolored compounds are resistant to reduction or bleaching by sodiumbisulfite. All of the substances I use are thus benzidines, or benzidinesalts, having substituents in the 3,3 positions, further qualified bytheir chemical behaviour when treated with potassium permanganatefollowed by sodium bisulfite.

Among the substances which can be used in the practice of the presentinvention are:

3,3 dichlorobenzidine and salts thereof 3,3 dibromobenzidine and saltsthereof 3,3 benzidine disulfonic acid and salts thereof 3,3dinitrobenzidine and salts thereof 3,3 diphenylbenzidine and saltsthereof All but the diphenyl compound are benzidines which aredisubstituted in the 3,3 positions by negative substituents, and allsuch negatively substituted benzidines form colored compounds withpermanganate which are resistant to removal when treated with sodiumbisulfite.

Salts of thesecompounds are generally the di-. hydrochloride such as 3,3dichlorobenzidine dihydrochloride since the hydrochlorides are readilywater soluble. The dinitro compounds are yellow but this is no objectionif the paper itself is tinted yellow or, when the nitro compound is usedfor printing warning indicia the printing is camouflaged as describedabove. All of these benzidine derivatives develop discernible brownishstains when treated with permanganate and the stain resists attempts toremove it by the application of a sodium bisulfite solution. The stainsalso resist attempts to remove them by volatilization.

The disubstituted benzidines of the present invention can beincorporated in the paper in any of the ways well known in the art. Oneof the simplest is to impregnate the paper with an aqueous solution ofthe disubstituted benzidine in the form of its water-solubledihydrochloride and then precipitate an insoluble salt by treating thepaper with an aqueous solution of an inorganic sulfate. Thisprecipitates the water-insoluble disulfate. Alternatively, the insolubledisubstituted benzidine sulfate can be added to the beater in themanufacture of the paper as a suspension. or aqueous suspensions of theinsoluble sulfate, such as 3,3 diciilorbenzidine sulfate can be used forsizing the paper.

.Proportions of the substituted benzidine are This is particularlyuseful where warning words or indicia which develop color upon theapplication of eradicators are printed. One suitable ink contains 2parts by weight of a 5% solution of ethyl cellulose in dimethylphthalateand 1 part of dichlorobenzidine. The ink vehicle used can be varied andis no part of the present invention. The proportions can, of course, bevaried over wide limits depending upon the printing conditions and thedesired depth of color in the resulting stain.

While the benzidine derivatives of the present invention areparticularly designed to be responsive to permanganate eradicators andresistant to attempts to remove the colored compounds thus formed, itwill, of course, be understood that the substances of my invention arehighly responsive to eradicators of the hypochlorite type. Thus I havebeen able to provide color-forming compounds for use in safety paperwhich are responsive to common ink eradicators and are resistant toattempts which may be made to remove the colored compounds formed.

The term safety paper" in the appended claims means any paper or writingsurface on which it is desired to indicate the application of a chemicalink eradicator by the production of a stain or discoloration.

Having thus described my invention, what I claim is:

1. Safety paper containing a benzidine compound chosen from the groupconsisting of substituted benzidines having negative substituents in the3,3 positions, and salts thereof.

2. Safety paper containing a 3,3 dihalo benzidine compound.

3. Safety paper containing a 3,3 dichlorobenzidine compound.

4. Safety paper containing a 3,3 diphenyl benzidine compound;

5. The process of preparing a. safety paper which comprisesincorporating in the paper a benzidine compound chosen from the groupconsisting of substituted benzidines, having negative substituents inthe 3,3 positions, and salts thereof.

6. The process of preparing a safety paper which comprises incorporatingin the paper a 3,3 dihalo benzidine compound.

'7. The process of preparing safety paper which comprises incorporatingtherein a 3,3 dichlorbenzidine compound.

8. The process of preparing safety paper which comprises incorporatingtherein a 3,3 diphenyl benzidine compound.

9. An ink comprising a vehicle and a benzidine compound chosen from thegroup consisting of substituted benzidines, having negative sub- BURGESSW. SMITH.

